1. Field of the Disclosure
The present invention pertains to apparatus employed in the delivery of a flow of breathing gas to the airway of a patient, and, more particularly, to pressure support system that automatically identifies a patient interface device that is coupled to a pressure generating system.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in their esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver continuous positive airway pressure (CPAP) or variable airway pressure, which varies with the patient's respiratory cycle, to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), or congestive heart failure.
Non-invasive ventilation and pressure support therapies involve the placement of a respiratory patient interface device, including a mask component, on the face of a patient. The mask component may be, without limitation, a nasal mask that covers the patient's nose, a nasal cushion having nasal prongs that are received within the patient's nares, a nasal/oral mask that covers the nose and mouth, or full face mask that covers the patient's face. The patient interface device interfaces the ventilator or pressure support device with the airway of the patient so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient.
It is common for users of pressure support devices to have several different patient interface devices (e.g., different masks and different patient interface components), tubing options, exhaust assemblies, or other component options (such as bacteria filters) that they use for reasons such as comfort. It is important for the pressure support device to know which type of patient interface device or other component is being used so that it will know certain information about the components, such as, without limitation, mask resistance, mask compliance, mask leak rates. Based on this information, the pressure support device can adjust the operating parameters of the unit. In addition, certain comfort features or device functions can be enabled on the basis of a particular mask or peripheral being attached.
Non-invasive ventilation and pressure support therapies are often based on a software driven mode that determines a breath-per-breath characteristic, such as, for example, the delivered or output pressure. The patient interface device being used often provides a specific exhaust flow pattern or characteristic, which is part of the computation of the output pressure. An effective and quick detection of the patient interface device in use and, hence, the exhaust flow characteristic can improve the accuracy of the output pressure computation.
A patient interface device typically includes three different types of leaks: total, intentional, and unintentional. The total leak is the sum of the intentional leak and the unintentional leak. The intentional leak is designed into the patient interface device (e.g., without limitation the exhaust assembly provided in the mask and/or patient circuit), in order that the patient does not re-breathe their own CO2. The unintentional leak is, for example, an annoying leak that hits the patient in the eyes. Hence, it is desired to minimize the unintentional leak. However, it is believed that unlike the total leak, the unintentional leak cannot be measured.
It is known to determine and report the unintentional leak by measuring the total leak while the patient is using the patient interface device (e.g., which total leak can be measured at the beginning of the night) and then subtracting the intentional leak.
It is known to detect the patient interface device in use with a ventilator by sensing the exhaust flow rate and looking for a specific flow pattern that is proportional to the pressure. See, for example, curve 1 in FIG. 1. In other words, such a ventilator looks for a specific flow point at a given pressure point. It is also known to employ different styles of patient interface devices that span a relatively large range of intentional leak rates. This involves several curves (not shown) like curve 1 of FIG. 1, which are parallel to one another. For reporting the type of patient interface device in use, there is a gradually increasing pressure test to determine if the device in use corresponds to a parallel curve (not shown) toward a bottom range, toward a middle range or toward an upper range of intentional leak. Based on this determination (upper, middle or bottom), the ventilator uses the corresponding intentional leak value (not shown) to subtract from the measured total leak in the calculation of the unintentional leak. However, it is believed that there is no change in therapy delivered by the ventilator, only in what it reports.